1. Field of the Invention
This invention relates to apparatus and methods for pressing or ironing a strip material, such as metal foil, as it is being wound onto the mandrel of a take-up reel and, more particularly, to such apparatus and methods wherein a constant force is applied to the growing coil by an ironing roll, and a constant distance is maintained between the point of contact of the ironing roll with the coil and the tangent point where the strip is wound onto the mandrel or coil, to avoid entrainment of air between overlapping wraps of the strip.
2. Description of Prior Art
The pressing or ironing of sheet or strip material by pressing a rotatable roll against a mandrel onto which the material is being wound is old in the art. It also is known to effect a constant pressing force of the roll against the mandrel or growing coil. For example, U.S. Pat. No. 4,404,831 provides a pressurizable hydraulic cylinder, concentrically surrounded by a pneumatic cylinder providing a constant spring characteristic for the compressed air in that cylinder. Rate of movement of the pressing roll relative to the mandrel or coil is controlled by controlling the velocity of fluid flow into the hydraulic cylinder, and the pressing force of the roll against the mandrel or coil is controlled by regulating the pressure of the hydraulic fluid.
In U.S. Pat. No. 4,736,605, an ironing roll pressure and position control mechanism is designed to avoid scrap loss of initially wound wraps due to the "hump" caused by the leading edge of the coiled strip. This is done by changing the pressure of the ironing roll against the coil as the "hump" on the rotating coil comes under the ironing roll, that is, the roll pressure is changed as a function of the position of the leading edge of the strip relative to the roll.
U.S. Pat. No. 4,964,587 discloses an apparatus for facilitating wrapping a strip of material on a mandrel, and comprises a first frame having a pivoted end and another end attached to a second, pivoted frame carrying a roller for pressing against the strip being wound and a curved guide plate for directing the strip onto the mandrel.
U.S. Pat. No. 5,275,345 relates to an ironing roll apparatus for winding metal foil and comprising a fluid pressure cylinder for moving the roll toward and away from the growing coil, and a pair of fluid pressure cylinders disposed at either end of the coil and actuable to adjust the roll at an angle to the width of the coil in order to correct improper coiling due to strip defects.
In the winding of very thin strip materials, such as aluminum foils and strip, e.g. of thicknesses on the order of 0.0003-0.030 inch, onto a mandrel, there is a tendency for the strip to flutter with accompanying air entrainment between the coil wraps which can cause defects in the coil during winding. This condition is to be avoided if possible. The above-mentioned U.S. Pat. No. 5,275,345 mentions this phenomenon and characterizes pressing or ironing rolls generally as functioning to reduce this air entrainment tendency by squeezing a portion of the air from between the wraps.